Since the first successful pregnancy following in vitro fertilization (IVF) was achieved in 1978, improvement in the techniques of assisted reproductive technologies has led to an increased success rate in the field of treating human infertility. Success in IVF programs is typically dependent upon the selection of the best embryo chosen for transfer to the uterus. Because of uncertainty in the functional viability of oocytes or early embryos, clinicians frequently transferred many embryos simultaneously. While improving the rate of pregnancy after IVF, this approach has also led to an increase in the rates of multiple pregnancies. The dangers of multiple pregnancies for both the mother and the neonates are well documented, and twin birth is now considered an undesirable outcome of IVF.
In the early years of IVF, embryo viability was considered to be a function of developmental progression during the pre-implantation phase. Over the last decade, the focus has been on the evaluation of certain morphological criteria of the oocyte or embryonic cells. The current approach to determining oocyte/embryo viability involves an indirect and subjective scoring system based on morphologically observable traits under a microscope [1, 2]. Scoring oocytes/embryos requires a highly skilled technician that takes the average clinical embryologist at least three months to learn. Although this approach has had some predictive value, it has been frequently criticized as imperfect and unreliable, generally thought to yield only a 23% average success rate. In many cases a selected oocyte or embryo may have normal morphology, as observed by the embryologist, but possess undetected alterations in their biochemistry that affect viability. For instance, oocytes invested with cumulus granulosa cells, called cumulus-oocyte complexes (COC), are not readily visible under a microscope because they are obscured underneath the cumulus cells, making viability grading difficult. The question of viability becomes more pronounced for cryopreserved cells once thawed. Furthermore, after fertilization, the combined sperm and egg form the zygote (a single cell embryo) in which dramatic functional changes take place that are not readily visible under conventional microscopes. One such current microscope relies on Hoffman modulation contrast that is used to visualize oocytes and zygotes.
However, currently there are no imaging modalities that capture the functional viability of oocytes, or early embryos prior to implantation inside the uterus.